Description:

Anthropogenic nitrogen (N) deposition can have a range of effects on terrestrial ecosystems, but these effects depend in part on the fate of this deposited N, particularly in the amount retained or lost from the system, and in the partitioning of retained N between plants and soils. We conducted a meta-analysis of studies at 48 sites around the world that used enriched 15N isotope tracers to examine the fate of N among ecosystem pools and to compare total ecosystem retention of N across sites. Most of these studies were conducted in North America (54%), followed by Europe (40%), Oceania (4%) and South America (2%). Forests were the most prevalent ecosystem type (63%), followed by grasslands (14%), tundra (12%), shrublands (8%) and wetlands (4%). In studies where N was added as a fertilizer (>2.5 kg N ha-1 yr-1), we determined the impact of the amount and form of fertilizer addition on ecosystem recovery of added 15N tracer. Our results demonstrate that the largest sinks for 15N were belowground, with the greatest N retention occurring in soil and litter pools. Factors that described the particular ecosystem and species (e.g., dominant vegetation growth form, mycorrhizal type, previous disturbance to the site), as well as procedural methods (e.g., form of 15N addition) had stronger effects on total ecosystem N retention than did climate (e.g., precipitation). In the short-term (<1 week following 15N tracer addition), elevation, mean annual temperature, organic C and N content and mineral soil C:N all explained a significant amount of variation in total ecosystem N retention. Natural abundance 15N of organic and mineral soil, as well as fine roots, were all negatively correlated with total ecosystem N retention. In the longer-term (>3 months to 1.5 year following 15N tracer addition), foliar natural abundance 15N was negatively correlated with total ecosystem N retention, while mineral soil C and N content and C:N ratios were positively correlated with total ecosystem N retention, suggesting dual control by organic matter content and stoichiometry. Overall, results of this study show that nitrogen additions lead to a significant decline in total ecosystem N retention, but the effect of fertilizer addition depends on the form and amount of N added.

Purpose/Objective:

Anthropogenic nitrogen (N) deposition can have a range of effects on terrestrial ecosystems, but these effects depend in part on the fate of this deposited N, particularly in the amount retained or lost from the system, and in the partitioning of retained N between plants and soils.

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Record Details:

Record Type: DOCUMENT (JOURNAL/PEER REVIEWED JOURNAL)

Start Date: 08/01/2012

Completion Date: 08/01/2012

Record Last Revised: 10/29/2012

Record Created: 03/18/2011

Record Released: 03/18/2011

OMB Category: Other

Record ID: 234112

Organization:

U.S. ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF RESEARCH AND DEVELOPMENT
NATIONAL HEALTH AND ENVIRONMENTAL EFFECTS RESEARCH LAB
WESTERN ECOLOGY DIVISION
FRESHWATER ECOLOGY BRANCH